The present invention relates to a cutting oil usable when cutting an object to be cut (including machined product) with a wire saw utilizing free abrasive grains, which can improve cutting performance and workability, a cutting oil composition comprising the cutting oil and an abrasive, a cutting method using the cutting oil composition, and a process for cleaning a wafer obtainable by the cutting method.
Conventionally, when a silicon ingot or the like is cut with a wire saw by utilizing free abrasive grains, to manufacture a sliced product, there is used a non-water-soluble cutting oil comprising a mineral oil as a main component. After the cutting, in order to clean to remove the clung non-water-soluble cutting oil which is deposited on the sliced product, there are employed organic solvents and specialized detergents.
In order to simplify cleaning of the above sliced product, there has been developed a water-soluble slicing oil agent (Japanese Patent Laid-Open No. Hei 3-181598 or the like). However, in the above water-soluble slicing oil agent, since there is a large change in viscosities caused by evaporation of water contained in the water-soluble slicing oil agent, temperature change, change in shearing rate of a wire saw, and the like, there is a defect that the cutting performance becomes poor. Further, the wafer obtained after cutting an ingot using the above water-soluble slicing oil agent is cleaned with water, and the waste water treatment after cleaning can be carried out by employing, for instance, aggregating sedimentation process, pressurized floatation process, activated sludge process, activated charcoal treatment process, or the like. However, all of these process have defects in that large costs and equipments therefor are necessitated.
In addition, since the abrasive grains which are used for abrasive grains (abrasives and the like) have a remarkably high specific gravity as compared to that of the cutting oil, the abrasive grains having high specific gravity are sedimented from the cutting oil composition in a slurry form, wherein the cutting oil composition comprises the cutting oil and the abrasive grains. Therefore, since the abrasive gains are sedimented inside the tank, pipe, or the like, the content of the abrasive grains is lowered, so that there arise problems that the cutting performance and the cutting accuracy are lowered, and that the sedimented and accumulated abrasive grains form a hard cake when the operation is stopped for a long period of time, thereby making it difficult to uniformly re-disperse the abrasive grains.
Accordingly, an object of the present invention is to provide a cutting oil which can give excellent dispersibility of an abrasive such as abrasive grains, and give excellent re-dispersibility when sedimented, cutting performance and workability; a cutting oil composition which can facilitate the cleaning of a cut product obtained after cutting; a cutting method using the cutting oil composition; a method of cutting an ingot; and a process for cleaning a wafer with a simple waste water treatment.
Specifically, the present invention relates to:
[1] a cutting oil comprising (a) a polyether compound represented by the formula (I):
R1O(EO)m(AO)nR2xe2x80x83xe2x80x83(I)
wherein each of R1 and R2, which may be identical or different, is hydrogen atom or a hydrocarbon group having 1 to 24 carbon atoms, at least one of which is a hydrocarbon group; EO is oxyethylene group; AO is an oxyalkylene group having 3 or 4 carbon atoms; and each of m and n is 1 to 50, wherein a sum of m and n is from 4 to 100;
[2] a cutting oil composition comprising the cutting oil of the above item [1] and an abrasive;
[3] a cutting method using the cutting oil composition of the above item [2]; and
[4] a process of cleaning a wafer comprising the steps of cleaning a wafer obtainable by cutting an ingot with a wire saw using the cutting oil composition of the above item [3]; heating the resulting waste water to a temperature equal to or higher than a cloud point of a polyether compound represented by the formula (I):
R1O(EO)m(AO)nR2xe2x80x83xe2x80x83(I)
wherein each of R1 and R2, which may be identical or different, is hydrogen atom or a hydrocarbon group having 1 to 24 carbon atoms, at least one of which is a hydrocarbon group; EO is oxyethylene group; AO is an oxyalkylene group having 3 or 4 carbon atoms; and each of m and n is 1 to 50, wherein a sum of m and n is from 4 to 100, the polyether compound being contained in waste water, to allow separation into an oil phase and an aqueous phase; and removing the oil s phase comprising the polyether compound from the waste water.